Toxic Bacillus pumilus from indoor air, recycled paper pulp, Norway spruce, food poisoning outbreaks and clinical samples

A New Landscape of Human Dental Aging: Causes, Consequences, and Intervention Avenues

Aging is accompanied by physical dysfunction and physiologic degeneration that occurs over an individual's lifetime. Human teeth, like many other organs, inevitably undergo chronological aging and age-related changes throughout the lifespan, resulting in a substantial need for preventive, restorative as well as periodontal dental care. This is particularly the case for seniors at 65 years of age and those older but economically disadvantaged. Dental aging not only interferes with normal chewing and digestion, but also affects daily appearance and interpersonal communications. Further dental aging can incur the case of multiple disorders such as oral cancer, encephalitis, and other systemic diseases. In the next decades or even hundreds of years, the proportion of the elderly in the global population will continue to rise, a tendency that attracts increasing attention across multiple scientific and medical disciplines. Dental aging will bring a variety of problems to the elderly themselves and poses serious challenges to the medical profession and social system. A reduced, but functional dentition comprising 20 teeth in occlusion has been proposed as a measurement index of successful dental aging. Healthy dental aging is critical to healthy aging, from both medical and social perspectives. To date, biomedical research on the causes, processes and regulatory mechanisms of dental aging is still in its infancy. In this article, updated insights into typical manifestations, associated pathologies, preventive strategies and molecular changes of dental aging are provided, with future research directions largely projected.

Characterization of Vegetative Bacillus cereus and Bacillus subtilis Strains Isolated from Processed Cheese Products in an Italian Dairy Plant

Processed cheese is a commercial product characterized by high microbiological stability and extended shelf life obtained through the application of severe heat treatment. However, spore-forming bacteria can survive through thermal processes. Among them, microorganisms belonging to Bacillus genus have been reported. In this study, we examined the microbiological population of the first hours' production of processed cheeses in an Italian dairy plant during two seasons, between June and October 2020. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to identify bacteria colonies, allowing the isolation of Bacillus cereus and Bacillussubtilis strains. These results were further confirmed by amplification and sequencing of 16 rRNA bacterial region. A multi-locus sequence type (MLST) analysis was performed to assess the genetic similarity among a selection of isolates. The fourteen B. cereus strains showed two sequence types: ST-32 was observed in only one strain and the ST-371 in the remaining thirteen isolates. On the contrary, all twenty-one B. subtlis strains, included in the study, showed a new allelic profile for the pycA gene, resulting in a new sequence type: ST-249. For B. cereus strains, analysis of toxin genes was performed. All isolates were positive for nheABC, entFM, and cytK, while hblABCD, bceT, and ces were not detected. Moreover, the biofilm-forming ability of B. cereus and B. subtilis strains was assessed, and all selected isolates proved to be biofilm formers (most of them were stronger producers). Considering the genetical similarity between isolates, jointly with the capacity to produce biofilm, the presence of a recurring Bacillus population could be hypothesized.

Case Report: Bacillus pumilus-Caused Bacteremia in a Patient with Food Poisoning

Bacillus pumilus has rarely been reported as a cause of human infections. We report a case of a B. pumilus causing food poisoning in an adult male. A 51-year-old Japanese man complained of severe abdominal cramps, fever with chills, diarrhea, dizziness, and loss of appetite after eating reheated rice with stewed minced meat purchased from a Kenyan restaurant. Bacillus pumilus was isolated from blood culture and was identified using a biochemical test and 16S rRNA gene sequencing analysis. The patient was treated with probiotics and ciprofloxacin and recovered after 3 days. To our knowledge, this is the first report describing the potential role of B. pumilus as a foodborne pathogen in Kenya and highlights the importance of good hygiene and food preparation practices.

Draft Genome Sequences of Sporulation-Impaired Bacillus pumilus Strain NRS576 and Its Native Plasmid p576

Bacillus pumilus spores can cause foodborne poisonings. B. pumilus strain NRS576 forms spores with a very reduced efficiency due to the presence of a plasmid, named p576.

Bacillus pumilus spores can cause foodborne poisonings. B. pumilus strain NRS576 forms spores with a very reduced efficiency due to the presence of a plasmid, named p576. Here, we report the genome sequence of strain B. pumilus NRS576 and its plasmid p576.

Increased mRNA expression of selected pro-inflammatory factors in inflamed bovine endometrium in vivo as well as in endometrial epithelial cells exposed to Bacillus pumilus in vitro

Endometrial epithelium plays a crucial role in the first immune response to invading bacteria by producing cytokines and chemokines. The aim of this study was to investigate the first inflammatory response of the endometrium in vivo and in vitro. Gene expression of several pro-inflammatory factors and Toll-like receptors (TLR2, -4, -6) was determined in endometrial cytobrush samples obtained from healthy cows and cows with clinical or subclinical endometritis. Endometrial epithelial cells were co-cultured with an isolated autochthonous uterine bacterial strain Bacillus pumilus. Total RNA was extracted from in vivo and in vitro samples and subjected to real-time reverse transcription polymerase chain reaction. CXC ligands (CXCL) 1/2 and CXC chemokine receptor (CXCR) 2 mRNA expression was higher in cows with subclinical endometritis and CXCL3 mRNA expression was higher in cows with clinical endometritis compared with healthy cows. B. pumilus induced cell death of epithelial cells within 24h of co-culturing. The presence of B. pumilus resulted in significantly higher mRNA expression of interleukin 1α (IL1A), IL6, IL8, CXCL1-3 and prostaglandin-endoperoxide synthase 2 in co-cultured cells compared with untreated controls. The maximum increase was mainly detected after 2h. These results support the hypothesis that bacterial infection of endometrial cells might induce prompt synthesis of pro-inflammatory cytokines resulting in a local inflammatory reaction.

Making soy sauce using direct fermentation of defatted soybean meal without the meju (soybean Koji) preparation process

Soy sauce prepared via direct fermentation of defatted soybean meal (DFSM) using halophiles without addition of dried, fermented soybeans or meju was evaluated. DFSM was fermented using single and mixed cultures of Oceanobacillus kimchii and Bacillus pumilus under 18% salinity conditions. Amounts of total organic nitrogen, free amino acids, and organic acids in soy sauce prepared with the mixed culture were slightly higher than sauces prepared with single culture. The ingredient content was higher in soy sauce prepared via direct fermentation of DFSM than soy sauce prepared with meju. Microorganisms detected in DFSM fermentation were not detected in the meju culture, except for the 2 halophiles, based on metagenomic analysis. Direct fermentation of DFSM is better than using meju for preparation of soy sauce.

The Prevalence and Control of Bacillus and Related Spore-Forming Bacteria in the Dairy Industry

Milk produced in udder cells is sterile but due to its high nutrient content, it can be a good growth substrate for contaminating bacteria. The quality of milk is monitored via somatic cell counts and total bacterial counts, with prescribed regulatory limits to ensure quality and safety. Bacterial contaminants can cause disease, or spoilage of milk and its secondary products. Aerobic spore-forming bacteria, such as those from the genera Sporosarcina, Paenisporosarcina, Brevibacillus, Paenibacillus, Geobacillus and Bacillus, are a particular concern in this regard as they are able to survive industrial pasteurization and form biofilms within pipes and stainless steel equipment. These single or multiple-species biofilms become a reservoir of spoilage microorganisms and a cycle of contamination can be initiated. Indeed, previous studies have highlighted that these microorganisms are highly prevalent in dead ends, corners, cracks, crevices, gaskets, valves and the joints of stainless steel equipment used in the dairy manufacturing plants. Hence, adequate monitoring and control measures are essential to prevent spoilage and ensure consumer safety. Common controlling approaches include specific cleaning-in-place processes, chemical and biological biocides and other novel methods. In this review, we highlight the problems caused by these microorganisms, and discuss issues relating to their prevalence, monitoring thereof and control with respect to the dairy industry.

Genomic analysis of a ginger pathogen Bacillus pumilus providing the understanding to the pathogenesis and the novel control strategy

Bacillus pumilus has been widely identified as a pathogen of plant and human, while the genetic information is rarely available for pathogenic B. pumilus strains. B. pumilus GR8 is a pathogen that causes ginger rhizome rot disease by invading ginger rhizome parenchymatous tissues, growing in the extracellular space, and producing plant cell wall-degrading enzymes to destroy ginger cells. In this study, the genome of GR8 was sequenced and characterized. This genome was the third completely sequenced genome of the B. pumilus species, and it exhibited high similarity to the genome of the B. pumilus strain B6033. The genome of GR8 was 3.67 Mb in length and encoded 3,713 putative ORFs. Among these predicted proteins, numerous plant cell wall-degrading enzymes and several proteins associated with invading and adapting to the environment in the extracellular space of the ginger rhizome parenchymatous tissue were found. The GR8 genome contained only one restriction-modification system and no CRISPR/Cas system. The lack of phage-resistant system suggested that phages might be potential agents for the control of GR8. The genomic analysis of GR8 provided the understanding to the pathogenesis and the phage-control strategy of pathogenic B. pumilus strains.

Surfactins in natto: the surfactin production capacity of the starter strains and the actual surfactin contents in the products

Surfactin-type lipopeptides are suspected of being implicated in the rare food poisonings caused by Bacillus species outside the Bacillus cereus cluster. In order to get information on surfactin levels in actual human foods, bacilli from three commercial samples of a Japanese traditional bean product, natto, were isolated in order to clarify their potential to produce the suspect lipopeptides. The isolated bacilli were characterized as Bacillus subtilis. They were β-hemolytic and gave a positive signal in the PCR screen for genes associated with surfactin production, and their culture extracts were cytotoxic to boar sperm cells. Organic extracts of both Bacillus cultures and the natto samples were analyzed for their surfactin content using ultrahigh-performance liquid chromatography with high-resolution mass spectrometry. All the strains proved to be surfactin producers (15 to 39 μg/ml culture medium); the natto samples contained as much as 2.2 mg g(-1) of surfactins. This means that consumers can ingest at least approximately 80 to 100 mg of surfactins per single 50-g natto serving apparently without suffering any ill effects, indicating a very low human toxicity.

Generation of biologically contained, readily transformable, and genetically manageable mutants of the biotechnologically important Bacillus pumilus

Bacillus pumilus mutants were generated by targeted deletion of a set of genes eventually facilitating genetic handling and assuring biological containment. The well-defined and stable mutants do not form functional endospores due to the deletion of yqfD, an essential sporulation gene; they are affected in DNA repair, as ΔuvrBA rendered them UV hypersensitive and, thus, biologically contained; they are deficient for the uracil phosphoribosyl-transferase (Δupp), allowing for 5-fluorouracil-based counterselection facilitating rapid allelic exchanges; and they are readily transformable due to the deletion of the restrictase encoding locus (ΔhsdR) of a type I restriction modification system. Vegetative growth as well as extracellular enzyme production and secretion are in no case affected. The combination of such gene deletions allows for development of B. pumilus strains suited for industrial use and further improvements.

Bacillus and relatives in foodborne illness

Species of Bacillus and related genera have long been troublesome to food producers on account of their resistant endospores. These organisms have undergone huge taxonomic changes in the last 30 years, with numbers of genera and species now standing at 56 and over 545, respectively. Despite this expansion, relatively few new species have been isolated from infections, few are associated with food and no important new agents of foodborne illness have been reported. What has changed is our knowledge of the established agents. Bacillus cereus is well known as a cause of food poisoning, and much more is now understood about its toxins and their involvement in infections and intoxications. Also, although B. licheniformis, B. subtilis and B. pumilus have occasionally been isolated from cases of food-associated illness, their roles were usually uncertain. Much more is now known about the toxins that strains of these species may produce, so that their significances in such episodes are clearer; however, it is still unclear why such cases are so rarely reported. Another important development is the use of aerobic endosporeformers as probiotics, as the potentials of such organisms to cause illness or to be sources of antibiotic resistance need to be borne in mind.

Toxinogenic and spoilage potential of aerobic spore-formers isolated from raw milk

The harmful effects on the quality and safety of dairy products caused by aerobic spore-forming isolates obtained from raw milk were characterized. Quantitative assessment showed strains of Bacillus subtilis, the Bacillus cereus group, Paenibacillus polymyxa and Bacillus amyloliquefaciens to be strongly proteolytic, along with Bacillus licheniformis, Bacillus pumilus and Lysinibacillus fusiformis to a lesser extent. Lipolytic activity could be demonstrated in strains of B. subtilis, B. pumilus and B. amyloliquefaciens. Qualitative screening for lecithinase activity also revealed that P. polymyxa strains produce this enzyme besides the B. cereus group that is well-known for causing a 'bitty cream' defect in pasteurized milk due to lecithinase activity. We found a strain of P. polymyxa to be capable of gas production during lactose fermentation. Strains belonging to the species B. amyloliquefaciens, Bacillus clausii, Lysinibacillus sphaericus, B. subtilis and P. polymyxa were able to reduce nitrate. A heat-stable cytotoxic component other than the emetic toxin was produced by strains of B. amyloliquefaciens and B. subtilis. Heat-labile cytotoxic substances were produced by strains identified as B. amyloliquefaciens, B. subtilis, B. pumilus and the B. cereus group. Variations in expression levels between strains from the same species were noticed for all tests. This study emphasizes the importance of aerobic spore-forming bacteria in raw milk as the species that are able to produce toxins and/or spoilage enzymes are all abundantly present in raw milk. Moreover, we demonstrated that some strains are capable of growing at room temperature and staying stable at refrigeration temperatures.

Biochemical and molecular characterization of Bacillus pumilus isolated from coastal environment in Cochin, India

Bacillus species constitute a diverse group of bacteria widely distributed in soil and the aquatic environment. In this study, Bacillus strains isolated from the coastal environment of Cochin, India were identified by detailed conventional biochemical methods, fatty acid methyl ester (FAME) analysis and partial 16S rDNA sequencing. Analysis of the data revealed that Bacillus pumilus was the most predominant species in the region under study followed by B. cereus and B. sphaericus. The B. pumilus isolates were further characterized by arbitrarily primed PCR (AP-PCR), antibiotic sensitivity profiling and PCR screening for known toxin genes associated with Bacillus spp. All B. pumilus isolates were biochemically identical, exhibited high protease and lipase activity and uniformly sensitive to antibiotics tested in this study. One strain of B. pumilus harboured cereulide synthetase gene cesB of B. cereus which was indistinguishable from rest of the isolates biochemically and by AP-PCR. This study reports, for the first time, the presence of the emetic toxin gene cesB in B. pumilus.

Acrebol, a novel toxic peptaibol produced by an Acremonium exuviarum indoor isolate

AIMS

To identify a toxin and its producer isolated from woody material in a building where the occupants experienced serious ill health symptoms.

METHODS AND RESULTS

Hyphal extracts of an indoor fungus, identified as the cycloheximide-tolerant species Acremonium exuviarum, inhibited motility of boar spermatozoa (EC(50) 5 +/- 2 microg of crude solids ml(-1)) and caused cytolysis of murine neuroblastoma cells (MNA) and feline fetal lung cells (FL). The responsible substances were purified and identified as two structurally similar, heat-stable, novel, toxic peptaibols, 1726 Da and 1740 Da, respectively, with amino acid sequences of Acetyl-Phe-Iva/Val-Gln-Aib-Ile-Thr-Leu-Aib-Pro-Aib-Gln-Pro-Aib-(X-X-X)-SerOH and Acetyl-Phe-Iva/Val-Gln-Aib-Ile-Thr-Leu-Val-Pro-Aib-Gln-Pro-Aib-(X-X-X)-SerOH. Purified acrebol inhibited motility of boar sperm, depleted ATP half-content in 1 day (EC(50) of 0.1 microg ml(-1), 60 nmol l(-1)) depolarised the mitochondria after 2 days, but did not affect the cellular content in NADH. This indicates mitochondrial toxicity. Plate-grown biomass of A. exuviarum BMB4 contained 0.1-1% (w/w) of acrebol, depending on the culture medium.

CONCLUSIONS

Acrebol paralysed the energy generation of mammalian cells suggesting that mitochondria were its target of action.

SIGNIFICANCE AND IMPACT OF THE STUDY

Acremonium exuviarum, as an indoor fungus, is potentially hazardous to health because of the toxic peptaibols that it produces.

Toxinogenic Bacillus pumilus and Bacillus licheniformis from mastitic milk

To elucidate the occurrence of heat-stable toxin-producing strains among mastitic Bacillus isolates, 100 milk samples of mastitic cows from different parts of Finland were screened. Bacillus was identified as the major organism in 23 samples. Toxinogenic Bacillus isolates identified by sperm cell motility inhibition assay were isolated from six samples. Four isolates belonged to the species Bacillus pumilus and two to Bacillus licheniformis. The toxic substances were heat-stable and soluble to methanol thus being of non-protein nature. The methanol extracted substances disrupted the sperm cell plasma membrane permeability barrier at exposure concentrations of 1-15 microg ml(-1) (B. pumilus) or 20-30 microg ml(-1) (B. licheniformis). The toxic properties of the two mastitic B. licheniformis strains were similar to those of B. licheniformis strains known to produce the lipopeptide lichenysin A and the synthetase genes lchAA, lchAB and lchAC for lichenysin were found in the mastitic strains by PCR. Toxin synthetase genes for the syntheses of lichenysin or surfactin were searched but not found in the toxic B. pumilus strains. The ribopatterns of the mastitic B. pumilus and B. licheniformis isolates were similar to those of the toxinogenic strains described earlier from food poisoning incidents and contaminated indoor air. B. licheniformis and B. pumilus survive pasteurization and other heat treatments as spores. Toxin-producing strains of these species in the dairy production chain may thus be of food safety concern.

Food poisoning associated with pumilacidin-producing Bacillus pumilus in rice

Food poisoning caused by other Bacillus species than B. cereus has been described, but the toxins involved have rarely been isolated. Endospores will survive heat treatment and will germinate and multiply in cooked foods producing toxins under appropriate conditions. We describe a small food poisoning outbreak where three people became ill after a dinner in a Chinese restaurant. Acute symptoms including dizziness, headache, chills and back pain developed during the meal, and a few hours later they got stomach cramps and diarrhoea which lasted for several days. Cooked, reheated rice was the prime suspect of the food poisoning, and from the rice large numbers of Bacillus pumilus were isolated. The isolated B. pumilus strain was found to produce a complex of lipopeptides known as pumilacidins with the highest amounts produced at 15 degrees C. This is the first report on isolation of a pumilacidin-producing B. pumilus strain from food implicated in food poisoning and characterization of the organism and the toxin complex involved.

Toxin-producing ability among Bacillus spp. outside the Bacillus cereus group

A total of 333 Bacillus spp. isolated from foods, water, and food plants were examined for the production of possible enterotoxins and emetic toxins using a cytotoxicity assay on Vero cells, the boar spermatozoa motility assay, and a liquid chromatography-mass spectrometry method. Eight strains produced detectable toxins; six strains were cytotoxic, three strains produced putative emetic toxins (different in size from cereulide), and one strain produced both cytotoxin(s) and putative emetic toxin(s). The toxin-producing strains could be assigned to four different species, B. subtilis, B. mojavensis, B. pumilus, or B. fusiformis, by using a polyphasic approach including biochemical, chemotaxonomic, and DNA-based analyses. Four of the strains produced cytotoxins that were concentrated by ammonium sulfate followed by dialysis, and two strains produced cytotoxins that were not concentrated by such a treatment. Two cultures maintained full cytotoxic activity, two cultures reduced their activity, and two cultures lost their activity after boiling. The two most cytotoxic strains (both B. mojavensis) were tested for toxin production at different temperatures. One of these strains produced cytotoxin at growth temperatures ranging from 25 to 42 degrees C, and no reduction in activity was observed even after 24 h of growth at 42 degrees C. The strains that produced putative emetic toxins were tested for the influence of time and temperature on the toxin production. It was shown that they produced putative emetic toxin faster or just as fast at 30 as at 22 degrees C. None of the cytotoxic strains produced B. cereus-like enterotoxins as tested by PCR or by immunological methods.

Description of heterotrophic bacteria occurring in paper mills and paper products

AIMS

To isolate aerobic mesophilic bacilli and thermophilic bacteria from different paper mill samples and to evaluate their potential harmfulness.

METHODS AND RESULTS

A total of 109 mesophilic and 68 thermophilic isolates were purified and characterized by automated ribotyping and partial 16S rDNA sequencing. The mesophilic isolates belonged to the genera Bacillus (13 taxa), Brevibacillus (three taxa) and Paenibacillus (five taxa). The thermophilic bacteria represented seven taxa of Bacillus, Geobacillus or Paenibacillus, four of proteobacteria and one of actinobacteria. The most frequently occurring bacteria were Bacillus cereus, B. licheniformis, Pseudoxanthomonas taiwanensis and bacteria closely related to Paenibacillus stellifer, P. turicensis or Leptothrix sp. One mill was contaminated throughout with bacteria of a novel mesophilic genus most closely related to Brevibacillus centrosporus and another with bacteria of a novel thermophilic genus most closely related to Hydrogenophilus thermoluteolus. One B. cereus isolate producing haemolytic diarrhoeal enterotoxin was detected and all the tested B. licheniformis isolates produced a metabolite toxic to boar sperm cells.

CONCLUSIONS

The bacilli and thermophilic bacteria isolated represent species which should not present occupational hazards in paper mill environments. The most harmful bacterium detected was B. licheniformis and potentially also B. cereus.

SIGNIFICANCE AND IMPACT OF THE STUDY

Knowledge of the microbial diversity in a paper mill provides a rational basis for development of an effective controlling programme. A database constructed from the fingerprints generated using automated ribotyping helps to identify and trace the contamination routes of bacteria occurring in paper mills.

Biological effects of Trichoderma harzianum peptaibols on mammalian cells

Trichoderma species isolated from water-damaged buildings were screened for toxicity by using boar sperm cells as indicator cells. The crude methanolic cell extract from Trichoderma harzianum strain ES39 inhibited the boar sperm cell motility at a low exposure concentration (50% effective concentration, 1 to 5 microg [dry weight] ml of extended boar semen(-1)). The same exposure concentration depleted the boar sperm cells of NADH(2). Inspection of the exposed boar sperm cells by transmission electron microscopy revealed damage to the plasma membrane. By using the black lipid membrane technique, it was shown that the semipurified metabolites (eluted from a SepPak C(18) cartridge) of T. harzianum strain ES39 induced voltage-dependent conductivity. The high-performance liquid chromatography-purified metabolites of T. harzianum strain ES39 dissipated the mitochondrial membrane potential (Deltapsi(m)) of human lung epithelial carcinoma cells (cell line A549). The semipurified metabolites (eluted from a SepPak C(18) cartridge) of T. harzianum strain ES39 were analyzed by mass spectrometry (MS). Matrix-assisted laser desorption ionization and nanoflow electrospray ionization MS revealed five major peptaibols, each of which contained 18 residues and had a mass ranging from 1,719 to 1,775 Da. Their partial amino acid sequences were determined by collision-induced dissociation tandem MS.

In vitro assay for human toxicity of cereulide, the emetic mitochondrial toxin produced by food poisoning Bacillus cereus

The in vitro boar spermatozoon test was compared with the LC ion trap MS analysis for measuring the cereulide content of a pasta dish, implemented in serious emetic food poisoning caused by Bacillus cereus. Both assays showed that the poisonous food contained approximately 1.6 microg of cereulide g(-1) implying the toxic dose in human as < or =8 microg kg(-1) body weight. The threshold concentration of cereulide provoking visible mitochondrial damage in boar sperm exposed in vitro was 2 ng of cereulide ml(-1) of extended boar sperm. The same threshold value was found for cereulide extracted from the food and from the cultured bacteria. This shows that other constituents of the food did not enhance or mask the effects of cereulide. Exposure of four human cell lines (HeLa, Caco-2, Calu-3 and Paju) to cereulide showed that the threshold concentration for the loss of mitochondrial membrane potential in human cells was similar to that observed in boar sperm. Human cells and boar sperm were equally sensitive to cereulide. The results show that boar spermatozoan assay is useful for detecting cereulide concentrations toxic to humans. Spermatozoa in commercially available extended fresh boar and cryopreserved bull semen were compared, boar sperms were 100 times more sensitive to cereulide than bull sperms.

Inhibition of human natural killer cell activity by cereulide, an emetic toxin from Bacillus cereus

The lipophilic toxin, cereulide, emitted by emetic food poisoning causing strains of Bacillus cereus, is a powerful mitochondria toxin. It is highly lipophilic and rapidly absorbed from the gut into the bloodstream. We tested how this toxin influences natural killer (NK) cells, which are important effectors in defence against infections and malignancy. Cereulide inhibited cytotoxicity and cytokine production of natural killer cells, caused swelling of natural killer cell mitochondria, and eventually induced natural killer cell apoptosis. The suppressive effect on cytotoxicity was fast and toxic concentration low, 20-30 microg/l. As the emesis causing concentration of cereulide is around 10 microg/kg of total body mass, our results suggest that emesis causing or even lower doses of cereulide may also have a systemic natural killer cell suppressive effect.

Toxic-metabolite-producing bacteria and fungus in an indoor environment

Toxic-metabolite-emitting microbes were isolated from the indoor environment of a building where the occupant was suffering serious building-related ill-health symptoms. Toxic substances soluble in methanol and inhibitory to spermatozoa at <10 microg (dry weight) ml(-1) were found from six bacterial isolates and one fungus. The substances from isolates of Bacillus simplex and from isolates belonging to the actinobacterial genera Streptomyces and Nocardiopsis were mitochondriotoxic. These substances dissipated the mitochondrial membrane potential (Deltapsi) of boar spermatozoa. The substances from the Streptomyces isolates also swelled the mitochondria. The substances from isolates of Trichoderma harzianum Rifai and Bacillus pumilus damaged the cell membrane barrier function of sperm cells.